The Flowbench thread.

As can be seen in the heads we are using on our engines the chamber modifications for big valve engines should be extensive.

I wouldn't feel too bad about the criticism, nobody escaped that.

In a few weeks time, I'm planning to visit darkspeed and his flow bench to assess the acclaims breathing, to achieve this a bracket is required to act on the valve





The head will get a clean-up next, but that will be over on my acclaim thread.

Covered previously with the main comment from me being that to get the most from the air figures getting into the engine everything else must also be fully optimised.

Many benches only test in one direction of flow - The bench I use flows in both directions - there is a reversal duct in the main motor chamber and an air flow direction changeover switch to the digital manometer sensors - For perfect results with the exhaust you have to get into the bench and flip the measuring orifice as these are knife edge calibrated plates that are only calibrated for one direction of flow - The other consideration is that you need to compensate for the air temp due to the heat generated by the motors.

However, there are few similarities between the condition on a bench when testing exhaust flow and those in the engine. The engine will pump those gasses out. The article referenced in a previous post about a Chesman Imp head development explains the importance of the exhaust valve/port flow and it also gives a hint as to why in the later Imp head developments they actually reduced the intake valve size so that they could get a bigger exhaust valve in.

There is a passage in the Vizard cylinderhead book about the Lotus twin cam - You could spend an age carefully gas flowing the intake and get a 5% increase in power - or you could just change the silencer for the same power increase - This due to the intake port efficiency being high as std. and the exhaust system efficiency being low as std in that particular end to end system.

If referring to the Carter head that's a swirl ramp - But there are other considerations with that head. As it is being filled by 1150cc of cylinder Carter had more aluminium in the chamber to "work with". There is a limited amount of material you can remove from the head - note the proximity of the valve seat insert to the squish pad opposite the plug - you cannot skim the head endlessly for compression - The smaller intake valve allows a bit more to be taken off the surface - with the 1.4 valve you would be into the seat insert which is not good. When working with small capacities it is easy to go shaping a chamber and end up with a too low a compression.

As shown in the testing above, to get the most from a big valve you need to unshroud the valve - bigger the valve the more material needs to be removed - The incline of the valves limits what you can skim off the deck. No point doing all that great work to get the perfect chamber and get left with 8.5:1 compression - that's not likely to work with a race cam looking for a 12:1 minimum static. Wills rings provide a better gas seal and are also thin so improve compression, these help as not only do we have material removed in the head for these big valves, we also have large cut outs in the top of the piston to compensate for.

Consider how you would get the compression back when its a 998 for a 1000cc class limit! - It's all deciding where you want to compromise.

Where Imp heads are concerned - A big valve head can result in very little or less gain in flow than a stock head unless dozens of hours have been spent with port and chamber optimisation.

One to test peeps knowledge

What's this off?

My guess was logicaluk's Honda engine, but it's definitely not that!

Back doing tests on the accumulated IMP stuff

Dropped the Carter 1150 head - 1.38 inlet - There was going to be a testing carried out on the exhaust flow on this head - but I was given the wrong size exhaust valve 1.125 instead of 1.2.






So flow on this head - 16" corrected to 28"

050 - 24
100 - 45
150 - 66
200 - 83
250 - 96
300 - 106
350 - 110
400 - 111
450 - 113


Then carried out a test with the Combined manifold and the BMW ITB - This test highlighted an issue with the BMW manifold that had been built up on the Derrington. The DCOE flange spacing is slightly different between the two manifolds.




050 - 23
100 - 45
150 - 64
200 - 80
250 - 91
300 - 99
350 - 101
400 - 102
450 - 103

I need to make a couple of comments on this test - The inlet valve had not been fully finished for shape - The valve is an REC 1.5 reduced to 138 and a simple 45 put on the end - it had not been shaped or profiled at all and this cam makes a difference at low lift flows between .050 and .100 lifts I think there will be a couple of CFM to find with the seat shape. It may also make a difference at higher lifts as well but that depends on the influence of any chamber shrouding.

Also worth noting that there was an amount of mismatch between the head and the manifold that would impact the higher flow numbers. There will be a couple of additional CFM to be had there.


The conversations that I have had with the whys and wherefores of the different valve configurations appear to be confirmed on the bench if we compare the Full race big inlet valve Chesman to the 1150 Carter - The inlet flows are not significantly different. But the allowance for the fitment of the big 1.2 exhaust is.

Now as I am sitting here typing this I have just realised that a standard Imp Intake valve is 1.2 and I probably have some of them so I could clean one up and give it some shape and run a flow comparison on the bench between the exhaust flow rates of these two heads.

During testing today I did do a flow reversal on the intake valve on the Carter the air flow and velocity out of that port is quite something.

I then dropped the Chesman head on the bench and ran the numbers on the Derrington manifolds - Test first with to confirm figure same as previously measured





Then the manifolds






The figures were identical for both

Slightly ported and stock Rad

200 - 82
250 - 93
300 - 102
350 - 107
400 - 110

The flow reduction measured is mainly down to the mismatch of the manifold and the port. Some simple port matching would get the figures up to the same or perhaps better than the head and radius alone.


Any Imp fanatic who is in the market for one of Derringtons featured in the tests - drop me a PM.

Shocking picture of the 1.2 inlet from a stock 533 Imp head - Given a quick clean up for test duties



Ready for the bench



On the bench



And a short clip of during test



Again test at 16 and numbers corrected to 28"

050 - 17CFM
100 - 31CFM
150 - 45CFM
200 - 55CFM
250 - 62CFM
300 - 66CFM
350 - 71CFM
400 - 74CFM

As this head is developed for a 410 lift Cam 450 - 76CFM

These figures are not calibrated flows as the plate is upside down in the bench but these are just for the back to back on the Chesman full race with the 1.125 and Carter 1.2

Edit.

I did a a calibration plate test on the reverse flow and it shows that the reading are 20% low due to the measuring plate not being in the correct orientation. I used a 100CFM plate and a 200 CFM plate and they both read 20% low. That should give actual readings for the figures above of -

050 - 20CFM
100 - 37CFM
150 - 54CFM
200 - 66CFM
250 - 74CFM
300 - 79CFM
350 - 85CFM
400 - 88CFM

And for the Carter that gives exhaust flow figures at .350" lift of Intake - 111CFM, Exhaust - 85CFM - Exhaust flow figure being 77% of the Intake flow figure. Roughly.